[PATCH v9 3/4] arm64: mte: add compression support to mteswap.c

[Catalin Marinas]

On Mon, Nov 13, 2023 at 11:52:32AM +0100, Alexander Potapenko wrote:
> Update mteswap.c to perform inline compression of memory tags when
> possible.
> 
> If CONFIG_ARM64_MTE_COMP is enabled, mteswap.c will attempt to compress
> saved tags for a struct page and store them directly in Xarray entry
> instead of wasting heap space.
> 
> Soon after booting Android, tag compression saves ~2x memory previously
> spent by mteswap.c on tag allocations. On a moderately loaded device with
> ~20% tagged pages, this leads to saving several megabytes of kernel heap:
> 
>   # cat /sys/kernel/debug/mteswap/stats
>   8 bytes:	102496 allocations,	67302 deallocations
>   128 bytes:	212234 allocations,	178278 deallocations
>   uncompressed tag storage size:	8851200
>   compressed tag storage size:	4346368
> 
> (statistics collection is introduced in the following patch)
> 
> Signed-off-by: Alexander Potapenko <glider at google.com>

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>